The present invention relates to a fuel injector. The following description will make explicit reference, without consequently losing its general nature, to an electromagnetic injector for direct fuel injection.
An electromagnetic fuel injector comprises a cylindrical tubular body with a central supply channel which performs the function of a fuel duct and ends with an injection jet controlled by an injection valve operated by an electromagnetic actuator. The injection valve is provided with a plunger, which is rigidly connected to a mobile armature of the electromagnetic actuator so as to be displaced by the action of the electromagnetic actuator between a closed position and an open position of the injection jet against the action of a spring which tends to hold the plunger in the closed position. The valve seat is defined by a sealing member, which is disc-shaped, seals the bottom of the central channel of the supporting body, and is passed through by the injection jet.
An electromagnetic fuel injector of the above-described type has been proposed, in which a guide member rises up from the sealing member, which guide member is tubular in shape, receives within it the plunger to define a lower guide for said plunger and has an external diameter smaller than the internal diameter of the supply channel of the supporting body, so as to define an external annular channel through which the pressurised fuel flows. In the lower part of the guide member, there are provided four through-holes which open into the valve seat to allow the pressurised fuel to flow towards said valve seat. The plunger ends in a sealing head, substantially spherical in shape, which is capable of resting in sealing manner against the valve seat and rests so as to slide on a cylindrical internal surface of the guide member so that it will be guided as it moves. The injection jet is defined by a single through-hole, which is arranged downstream from the valve seat and passes through the sealing member.
With the aim of improving the performance of the above-described injector by producing an injection jet with a complex geometry, a new type of injector has subsequently been proposed, in which the guide member has an external diameter which is substantially equal to the internal diameter of the supply channel of the supporting body; recesses are provided in the sealing head in such a manner as to define channels between each recess and the internal cylindrical surface of the guide member which permit the fuel to pass towards the injection jet. The injection jet is of the “multi-hole” type, i.e. is defined by a plurality of through-holes, which are made starting from a hemispherical chamber made downstream from the valve seat; in this manner, it is possible to achieve optimum injection jet geometries for various applications by appropriately directing the individual through-holes.
Experimental testing has revealed that, when in service, the above-described electromagnetic fuel injector has a tendency to form an excessive quantity of fouling in the vicinity of the injection jet. Such fouling may bring about the partial or complete blockage of the through-holes of the injection jet, with an obvious negative impact on injector performance; in other words, the performance of such an injector tends to deteriorate too rapidly, unacceptably shortening the service life of the injector.
US2004055566A1 discloses a fuel injector for the direct injection of fuel into a combustion chamber of an internal combustion engine; the fuel injector has a valve needle, that has at its injector end a valve-closure member that works together with a valve-seat surface, formed on a valve-seat member, to form a sealing seat, and has at least one swirl duct, a swirl chamber formed on the valve-seat member, and a plurality of injection openings that open out from the swirl chamber, through which the fuel, provided with a swirl, is simultaneously injected.
US2003116658A1 discloses a fuel injector for the direct injection of fuel into a combustion chamber of an internal combustion engine; the fuel injector includes an actuator for actuating a valve needle, the valve needle having on an injection-side end a valve-closure member which forms a sealing seat together with a valve-seat surface, which is formed on a valve-seat member. Fuel channels are arranged in a valve needle guide, connected to the valve-seat member or designed as a single piece with it, in several rows circumferentially in the valve needle guide, at least one row of fuel channels being arranged, in the resting state of the fuel injector, above a guide line of the valve-closure member.